DE102016218235A1 - Process for the preparation of propanol, propionaldehyde and / or propionic acid from carbon dioxide, water and electrical energy - Google Patents

Abstract

The present invention relates to a process for the preparation of propanol, propionaldehyde and / or propionic acid, in which CO and C2H4 are provided from an electrolysis of CO2, and preferably hydrogen is also provided electrolytically, and the CO and C2H4 with H2 to propanol and / or Propionaldehyde and / or the CO and C2H4 are reacted with H2O to propionic acid.

Description

The present invention relates to a process for the preparation of propanol, propionaldehyde and / or propionic acid in which CO and C ₂ H _{4 are provided} from an electrolysis of CO ₂ , and preferably also electrolytically hydrogenated, and the CO and C ₂ H ₄ with H ₂ to propanol and / or propionaldehyde and / or the CO and C ₂ H ₄ are reacted with H ₂ O to propionic acid.

The burning of fossil fuels currently covers about 80% of global energy needs. In 2011, these combustion processes emitted around 34,032.7 million tonnes of carbon dioxide (CO ₂ ) into the atmosphere worldwide. This release is the easiest way to dispose of even large amounts of CO ₂ (lignite power plants over 50000 tons per day).

The discussion about the negative effects of the greenhouse gas CO ₂ on the climate has led to a reflection on the recycling of CO ₂ . Thermodynamically, CO _{2 is} very low and can therefore be reduced back to useful products.

In nature, CO _{2 is} converted into carbohydrates by photosynthesis. This temporally and on a molecular level spatially divided into many sub-steps process is very difficult to copy on an industrial scale. The currently more efficient way compared to pure photocatalysis is the electrochemical reduction of CO _2. A mixed form is light-assisted electrolysis or electrically assisted photocatalysis. Both terms are synonymous to use, depending on the perspective of the viewer.

As with photosynthesis, CO _{2 is transformed} into an energetically higher value product (such as CO, CH ₄ , C ₂ H ₄ , etc.) By supplying electrical energy (possibly photo-assisted) from regenerative energy sources such as wind or sun .) transformed. The amount of energy required in this reduction ideally corresponds to the combustion energy of the fuel and should only come from renewable sources. An overproduction of renewable energies is not continuously available, but currently only at times with strong sunlight and strong wind. However, this will continue to increase in the near future as renewable energy continues to expand.

Currently, the electrification of the chemical industry is discussed. This means that chemical precursors or fuels are preferably to be produced from CO ₂ (CO), H ₂ O while supplying excess electrical energy, preferably from regenerative sources. In the introductory phase of such a technology, the aim is that the economic value of a substance is significantly greater than its calorific value (calorific value).

Electrolysis processes have evolved significantly in recent decades. The PEM water electrolysis could be optimized to high current densities, and large electrolysers with megawatts of performance will be launched on the market.

An example of chemical precursors are propionaldehyde and propionic acid.

Propionaldehyde is usually obtained by hydroformylation of ethene / ethylene: C ₂ H ₄ + CO + H ₂ → CH ₃ -CH ₂ -CHO

Propanol can also be provided with two equivalents, for example with [HCo (phosphine) (CO) ₃ ] as catalyst.

Both ethylene and H ₂ and CO are usually produced from fossil sources.

For example, ethylene is obtained from steam cracking of naphtha (1st crude oil distillate).

• – Kohlevergasung: C + ½O₂ → CO; C + H₂O → CO + H₂ oder
• – Dampfreformierung von Methan: CH₄ + H₂O → CO + 3H₂

gewinnen. CO in turn you can, for example, by

• - coal gasification: C + ½O ₂ → CO; C + H ₂ O → CO + H ₂ or
• - Steam reforming of methane: CH ₄ + H ₂ O → CO + 3H ₂

win.

However, this latter CO: H ₂ ratio is not suitable for the hydroformylation.

Hydrogen (H ₂ ) can be obtained, for example, by the water gas shift reaction: CO + H ₂ O → CO ₂ + H ₂ .

Alternatively, propionaldehyde and propionic acid can also be prepared by hydration of propene and then subsequent oxidation. Another method is the propanol oxidation.

However, all of these processes for educt production consume fossil energy, lead to by-products and / or do not take place in a suitable phase to carry out the hydroformylation or are very complex.

The electrochemical reduction of CO ₂ to solid-state electrodes in aqueous electrolyte solutions offers a multitude of product possibilities which are described in the following Table 1, taken from Y. Hori, Electrochemical CO ₂ reduction on metal electrodes, in: C. Vayenas, et al. (Eds.), Modern Aspects of Electrochemistry, Springer, New York, 2008, pp. 89-189 , are shown. Table 1: Faraday efficiencies for carbon dioxide on various metal electrodes electrode CH ₄ C ₂ H ₄ C ₂ H ₅ OH C ₃ H ₇ OH CO HCOO ^- H ₂ Total Cu 33.3 25.5 5.7 3.0 1.3 9.4 20.5 103.5 Au 0.0 0.0 0.0 0.0 87.1 0.7 10.2 98.0 Ag 0.0 0.0 0.0 0.0 81.5 0.8 12.4 94.6 Zn 0.0 0.0 0.0 0.0 79.4 6.1 9.9 95.4 Pd 2.9 0.0 0.0 0.0 28.3 2.8 26.2 60.2 ga 0.0 0.0 0.0 0.0 23.2 0.0 79.0 102.0 pb 0.0 0.0 0.0 0.0 0.0 97.4 5.0 102.4 hg 0.0 0.0 0.0 0.0 0.0 99.5 0.0 99.5 In 0.0 0.0 0.0 0.0 2.1 94.9 3.3 100.3 sn 0.0 0.0 0.0 0.0 7.1 88.4 4.6 100.1 CD 1.3 0.0 0.0 0.0 13.9 78.4 9.4 103.0 tl 0.0 0.0 0.0 0.0 0.0 95.1 6.2 101.3 Ni 1.8 0.1 0.0 0.0 0.0 1.4 88.9 92.4 Fe 0.0 0.0 0.0 0.0 0.0 0.0 94.8 94.8 Pt 0.0 0.0 0.0 0.0 0.0 0.1 95.7 95.8 Ti 0.0 0.0 0.0 0.0 0.0 0.0 99.7 99.7

In the DE 10 2015 203 245.0 It has been disclosed that high ethylene efficiencies can be achieved even at industrially relevant current densities above 150 mA / cm ² . As by-products, however, still small amounts of CO and / or significant amounts of H _{2 may be} incurred. If pure substances such as ethylene are to be obtained, the process thus possibly requires a further purification step.

Furthermore, processes are needed with which basic chemical building blocks such as propionaldehyde and propionic acid can be effectively recovered.

The inventors have found that propanol, propionaldehyde or propionic acid are effectively produced when all the necessary raw materials for propanol, propionaldehyde or propionic acid synthesis are produced electrochemically. In particular, a synthesis process for propanol, propionaldehyde or propionic acid with as few steps and low temperature is described. For slightly elevated temperatures below 100 ° C, preferably below 80 ° C even the waste heat of the electrolyzer can be used.

In a first aspect, the present invention relates to a process for the preparation of propanol, propionaldehyde and / or propionic acid comprising: electrolysis of CO ₂ to CO and C ₂ H ₄ ; and implementation of CO and C ₂ H ₄ with H ₂ to propanol and / or propionaldehyde, and / or reaction of CO and C ₂ H ₄ with H ₂ O to propionic acid.

Furthermore, in a further aspect, the present invention relates to an apparatus for producing propanol, propionaldehyde and / or propionic acid, comprising: at least one first electrolyzer for the electrolysis of CO ₂ to CO and C ₂ H ₄ , which is designed to CO and C ₂ H ₄ to produce by electrolysis of CO ₂ ; and at least one first reactor for the reaction of CO and C ₂ H ₄ with H ₂ to propanol and / or propionaldehyde, and or for the reaction of CO and C ₂ H ₄ with H ₂ O to propionic acid.

In a further aspect, the present invention relates to a device for producing propanol, propionaldehyde and / or propionic acid, comprising:
at least one first electrolysis device for the electrolysis of CO ₂ and / or CO to C ₂ H ₄ , which is designed to produce C ₂ H ₄ by electrolysis of CO ₂ and / or CO;
at least one second electrolysis device for the electrolysis of CO ₂ to CO, which is designed to produce CO by electrolysis of CO ₂ ; and
at least one first reactor for the reaction of CO and C ₂ H ₄ with H ₂ to propanol and / or propionaldehyde, and / or for the reaction of CO and C ₂ H ₄ with H ₂ O to propionic acid.

Further aspects of the present invention can be found in the dependent claims and the detailed description.

The accompanying drawings are intended to illustrate embodiments of the present invention and to provide a further understanding thereof. In the context of the description, they serve to explain concepts and principles of the invention. Other embodiments and many of the stated advantages will become apparent with reference to the drawings.

The elements of the drawings are not necessarily to scale. Identical, functionally identical and identically acting elements, features and components are in the figures of the drawings, unless otherwise stated, each provided with the same reference numerals.

1 - 5 schematically show exemplary representations of a possible construction of an electrolytic cell according to an embodiment of the present invention.

6 schematically shows an embodiment of an electrolysis system for CO ₂ reduction without the inventive design of the connection between the electrolyte supply and gas diffusion electrode.

7 schematically shows an embodiment of an electrolysis plant for CO ₂ reduction with gas diffusion electrode.

8th schematically shows the sequence of a process according to the invention for propionaldehyde production.

In a first aspect, the present invention relates to a process for the preparation of propanol, propionaldehyde and / or propionic acid, comprising:
Electrolysis of CO ₂ to CO and C ₂ H ₄ ; and
Reaction of CO and C ₂ H ₄ with H ₂ to propanol and / or propionaldehyde, and / or reaction of CO and C ₂ H ₄ with H ₂ O to give propionic acid.

Produced propanol, if not sold directly, may be converted to propionaldehyde and / or propionic acid after storage by oxidation, if necessary.

The present process represents a very efficient example of the electrification of the chemical industry. Electrification of the chemical industry in this case means that from CO ₂ , H ₂ O and electricity (for electrolysis), especially electricity surpluses, preferably from renewable sources, raw materials the chemical industry. The preparation of propanol and / or propionaldehyde is a prime example of this. Due to side reactions and selectivities, the CO ₂ electrolysers normally deliver well below 100% gas mixtures, which actually need to be purified for sale and / or further use.

However, for the preparation of propanol and / or propionaldehyde, these mixtures need not be purified or separated, except where appropriate for the removal of excess CO ₂ , since the mixture according to certain embodiments suitably from ethylene, CO and H ₂ , so for use for a hydroformylation or Propanol production, or at least only certain proportions of a component must be added.

In the process, ethene can be prepared electrolytically both from CO ₂ and from CO, which can be obtained from CO ₂ , so that a sequential sequence of the electrolyses is possible, wherein at least a portion of the CO initially produced is converted to C ₂ H ₄ or a parallel electrolysis of CO ₂ to ethene and CO may take place. Also, ethene can be produced simultaneously from CO and CO ₂ , depending on the availability of different electrolyzers. It is also not excluded to use CO from external sources for electrolysis in addition to CO ₂ , if there is an excess of CO in an external source.

The particular electrolysis of the CO ₂ and / or CO is not particularly limited and may suitably with one or more corresponding electrolysis cells or electrolysis vonstattengehen.

An electrolysis process is particularly interesting because it is a one-step process in which from almost worthless, climate-damaging CO ₂ and CO can be obtained with the help of electricity energy sources or chemical precursors.

For example, CO can be obtained with high selectivity on silver catalysts. Ethene, on the other hand, can be formed on copper-based electrodes. Thus, according to certain embodiments, the production of C ₂ H ₄ from CO ₂ and / or CO is carried out by electrolysis on a copper-containing cathode which comprises copper or consists of copper. According to certain embodiments, the production of CO from CO2 is carried out by electrolysis at a cathode comprising a metal or consisting of a metal selected from the group consisting of Au, Ag and / or Zn, preferably Ag. Preferably, a silver-containing cathode is used for CO production, which may for example also consist of Ag.

In the electrochemical ethylene production from CO ₂ , as described, in addition, the intermediate CO be run through, such as in DE 10 2016 200 858.7 shown in detail.

The production of ethene and CO can be carried out in an electrolysis cell or an electrolysis device, for example, alternately the cathode can be replaced to produce different product gases, but can also be done in two or more electrolysis cells or electrolysis, the respective products obtained Ethene and CO, which may for example be mixed in water or provided with moisture, can be suitably mixed before the reaction to propanol, propionaldehyde and / or propionic acid.

Hydrogen can also be produced, for example, from an electrolysis of water on platinum-containing cathodes, but also often arises as a by-product in the electrolysis of CO ₂ , as can be seen from Table 1 above, so that, if necessary, no separate H ₂ -electrolyser is required.

For example, therefore, the electrolytically produced ethylene and CO, or by the competition reaction with H ₂ O, H ₂ included. Co produced, for example, on silver electrodes also contains small to substantial amounts of H ₂ .

According to certain embodiments, H _{2 is} thus provided by the electrolysis of CO ₂ and / or an electrolysis of H ₂ O. The electrolysis of water is here, as well as the electrolysis of CO ₂ , not particularly limited and may include conventional electrolysis of water.

Exemplary reactions in the electrolysis to produce CO, ethene and hydrogen are as follows.

The required cathode reactions for this are, for example: Hydrogen: 2H ₂ O + 2e ^- → H ₂ + 2OH ^- Carbon monoxide: CO ₂ + 2e ^- + H ₂ O → CO + 2OH ^- ethylene: 2CO ₂ + 12e ^- + 8H ₂ O → C ₂ H ₄ + 12OH ^-

These cathode reactions can be combined in virtually any way with different anode reactions.

• – Chloralkalierzeugung: 2Cl^– → Cl₂ + 2e^–

Examples are:

• - Chloroalcohol production: 2Cl ^- → Cl ₂ + 2e ^-

• – Sauerstofferzeugung: 2H₂O – 4e^– → O₂ + 4H⁺
• – Wasserstofferzeugung: 2H₂O – 2e^– → H₂O₂ + 2H⁺
• – Peroxodisulfaterzeugung: 2SO₄ ^2– – 2e^– → S₂O₈ ^2–

It can, as in DE 10 2015 212 504.1 described, considerable amounts of valuable NaHCO ₃ incurred, which can be further processed to soda.

• - Oxygen production: 2H ₂ O - 4e ^- → O ₂ + 4H ⁺
• - Hydrogen production: 2H ₂ O - 2e ^- → H ₂ O ₂ + 2H ⁺
• - Peroxodisulfaterzeugung: 2SO ₄ ^2- - 2e ^- → S ₂ O ₈ ^2-

At the anode produced oxygen compounds such as O ₂ , peroxides such as peroxodisulfate can be used for the oxidation of propanol and / or propionaldehyde to propionic acid, whereby the synergy of the overall process is underlined again. In this case, waste heat from the electrolysis or the electrolysis devices for the oxidation of the propanol and / or propanals / propionaldehyde, for example propanal, for example in the presence of cobalt or manganese ions, for example at 40-50 ° C, may be used according to certain embodiments. This oxidation can take place in a second reactor of the devices according to the invention. From the propanol and / or propionaldehyde can therefore be prepared by including the anode reaction propionic acid itself.

According to certain embodiments, an oxygen species is thus also generated anodically in the process according to the invention during the electrolysis of CO ₂ , and the oxygen species can be reacted with propanol and / or propionaldehyde to form propionic acid. According to certain embodiments, the oxygen species is oxygen and / or a peroxide such as hydrogen peroxide or a peroxodisulfate.

As shown above, the electrolysis methods and the electrolysis cells or electrolysis units / electrolysis units / electrolyzers used therefor are not particularly limited.

The individual electrolyzers can be designed differently.

As a hydrogen electrolyzer, for example, those with a polymer electrolyte membrane, and / or alkali or chloralkali electrolysers are conceivable.

The electrolytes of the CO ₂ electrolysers contain, according to certain embodiments, alkali metal cations, more preferably Na ⁺ and / or K ⁺ . As anions, for example, carbonate, bicarbonate, sulfate, hydrogen sulfate and / or phosphates are preferred. These can be suitably selected depending on the anodic reaction. The electrolytes may also contain or consist of additives such as ionic liquids.

1 - 5 show exemplary representations of a possible structure of an electrolytic cell, for example for the reduction of carbon dioxide or carbon monoxide reduction, which in the process according to the invention and the devices according to the invention can be used, wherein the anode and cathode regions can be combined with each other as desired.

The electrolysis cell of an electrolysis device in the devices according to the invention, which can be used in the method according to the invention, comprises at least one anode and one cathode, one of which may be formed as a gas diffusion electrode, for example, and a cell space adapted to be filled with an electrolyte and in which the anode and the cathode are at least partially incorporated. It is not excluded according to the invention that both the anode and the cathode are formed as a gas diffusion electrode. According to certain embodiments, the anode is formed as a gas diffusion electrode. According to certain embodiments, the cathode is designed as a gas diffusion electrode. According to certain embodiments, carbon dioxide and / or carbon monoxide is electrolytically reacted in the carbon dioxide electrolysis or carbon monoxide electrolysis at the cathode, that is, the cathode is designed such that it can convert carbon dioxide and / or carbon monoxide, for example as copper- and / or silver-containing gas diffusion electrode.

The electrolysis cells used correspond, for example, to those which are shown schematically in FIG 1 to 5 are shown, wherein in the figures cells are shown with membrane M, which may also be absent in the devices according to the invention, according to certain embodiments, but application and which can separate an anode compartment I and a cathode compartment II. As a membrane is present, this is not particularly limited and adapted for example to the electrolysis, for example, the electrolyte and / or the anode and / or cathode reaction.

The electrochemical reduction, for example of CO ₂ , takes place in an electrolysis cell, which usually consists of an anode and a cathode compartment. In the 1 to 5 Examples of a possible cell arrangement are shown. For each of these cell arrangements, a gas diffusion electrode may be used, for example as a cathode.

Exemplary is the cathode compartment II in 1 and 2 designed such that a catholyte is supplied from below and then leaves the cathode space II upwards. Alternatively, however, the catholyte can also be supplied from above, as for example with falling film electrodes. At the anode A, which is electrically connected to the cathode K by means of a current source for providing the voltage for the electrolysis, takes place in the anode compartment I, the oxidation of a substance, which is supplied from below, for example with an anolyte, and the anolyte with the product the oxidation then leaves the anode compartment. In the in 1 and 2 a reaction gas such as carbon dioxide and / or carbon monoxide through and / or along a cathode, for example a gas diffusion electrode, here exemplified the cathode K, are promoted in the cathode space II for the reduction, for example as in 1 (In Hinterströmbetrieb, so the cathode is designed as a gas diffusion electrode) or in Durchströmbetrieb in 2 (with gas diffusion electrode). Although not shown but also embodiments with porous anode A are conceivable. In 1 and 2 the spaces I and II are separated by a membrane M. In contrast, in the PEM (proton or ion exchange membrane) structure of the 3 the cathode K, for example, a gas diffusion electrode, and a, for example, porous, anode A directly to the membrane M, whereby the anode compartment I is separated from the cathode compartment II. The construction in 4 corresponds to a mixed form of the structure 2 and the structure 3 , wherein on the catholyte side a structure with the gas diffusion electrode and gas supply G is provided in Durchströmbetrieb, as in 2 whereas, on the anolyte side, a structure as in FIG 3 is provided. Of course, mixed forms or other embodiments of the exemplified electrode spaces are conceivable. Also conceivable are embodiments without membrane. According to certain embodiments, the cathode-side electrolyte and the anode-side electrolyte may thus be identical, and the electrolysis cell / electrolysis unit may possibly manage without a membrane, but preferably a membrane for gas separation is present. However, it is thus not excluded that the electrolytic cell has a membrane in such embodiments, but this is associated with additional expense in terms of the membrane as well as the applied voltage. Catholyte and anolyte can also optionally be mixed again outside the electrolysis cell.

5 corresponds to the structure of 4 , where here the gas supply G takes place in Hinterströmbetrieb and the Edukt- and product passage E and P are shown.

1 to 5 are schematic representations. The electrolysis cells off 1 to 5 can also be combined to mixed variants. For example, the anode compartment may be in the form of a PEM half cell, as in FIG 3 , while the cathode compartment consists of a half-cell containing a certain volume of electrolyte between the membrane and the electrode, as shown in FIG 1 shown. The membrane can also be designed in multiple layers, so that separate supply of anolyte or catholyte is made possible. Separation effects are achieved in aqueous electrolytes, for example by the hydrophobicity of intermediate layers. Nevertheless, conductivity can be ensured if conductive groups are integrated in such separation layers. The membrane may be an ion-conducting membrane, or a separator, which causes only a mechanical separation, for example gas separation, and is permeable to cations and anions.

By using a gas diffusion electrode, it is possible to construct a three-phase electrode. For example, a gas can be guided from the rear to the electrically active front side of the electrode in order to carry out an electrochemical reaction there. According to certain embodiments, the gas diffusion electrode can also only be trailing behind, ie a gas such as CO ₂ and / or CO is guided past the rear side of the gas diffusion electrode in relation to the electrolyte, wherein the gas can then penetrate through the pores of the gas diffusion electrode and the product is discharged at the rear can. Preferably, the gas flow during the backflow is inversely to the flow of the electrolyte, so that depressed liquid such as electrolyte can be removed.

• a. ein Gas wie CO₂ und/oder CO wird durch die Kathode gedrückt.
• b. ein Gas wie CO₂ und/oder CO fließt hinter der Kathode vorbei.

The gas diffusion electrodes, eg for high current densities, can thus operate in two fundamentally different operating modes:

• a. a gas such as CO ₂ and / or CO is forced through the cathode.
• b. a gas such as CO ₂ and / or CO flows past the cathode.

An exemplary electrolysis device for CO ₂ electrolysis is in 6 is shown analogous but also for example for a CO electrolysis conceivable.

It is shown an electrolysis device in which carbon dioxide is reduced on the cathode side and is oxidized on the anode A side water. Alternatively, a reaction of chloride to chlorine, bromide to bromine, sulfate to peroxodisulfate (with or without gas evolution), etc. could take place on the anode side. For example, platinum is suitable as anode A, and copper as cathode K. The two electrode chambers of the electrolytic cell are separated in the Figure by a membrane M, such as Nafion ^®. The integration of the cell into a system with anolyte circulation 10 and catholyte circulation 20 is shown in the figure.

Anodense is placed in an electrolyte reservoir 12 Water with electrolyte additives via an inlet 11 fed. However, it is not excluded that water in addition to or instead of the inlet 11 at another location of the anolyte circuit 10 is supplied, as in accordance with 6 the electrolyte reservoir 12 can also be used for gas separation. From the electrolyte reservoir 12 becomes water / electrolyte by means of the pump 13 pumped into the anode compartment where it is oxidized. The product is then returned to the electrolyte reservoir 12 pumped where it is in the product gas tank 26 can be dissipated. Via a product gas outlet 27 the product gas can be added to the product gas container 26 be removed. Of course, the separation of the product gas can also be done elsewhere. This results in an anolyte circuit 10 because the electrolyte is also circulated on the anode side.

On the cathode side is in the catholyte circuit 20 Carbon dioxide via a CO ₂ inlet 22 in an electrolyte storage tank 21 introduced, where it is, for example, physically solved. By means of a pump 23 This solution is placed in the cathode compartment, where the carbon dioxide is reduced at the cathode K, for example to CO on a silver cathode. An optional additional pump 24 then pumps the solution obtained at the cathode K containing CO further to a vessel for gas separation 25 where the product gas containing CO in a product gas container 26 can be dissipated. Via a product gas outlet 27 the product gas can be added to the product gas container 26 be removed. The electrolyte is in turn from the container for gas separation back to the electrolyte reservoir 21 pumped, where again carbon dioxide can be added. Again, only an exemplary arrangement of a catholyte circuit 20 indicated, wherein the individual device components of the catholyte cycle 20 can also be arranged differently, for example by the gas separation is already carried out in the cathode compartment. Preferably, the gas separation and the gas saturation are carried out separately ie in one of the containers, the electrolyte is saturated with CO ₂ and then pumped as a solution without gas bubbles through the cathode compartment. The gas that emerges from the cathode compartment, then consists of a predominant proportion of CO, since CO ₂ itself remains dissolved because it was consumed and thus the concentration in the electrolyte is slightly lower.

The electrolysis takes place in 6 by adding power through a power source, not shown.

In order to be able to supply the water and the dissolved CO ₂ in the electrolyte with time-varying pressure of the electrolysis, can in the anolyte 10 and catholyte circulation 20 valves 30 brought in be, which are controlled by a control device, not shown, and thus control the supply of anolyte and catholyte to the anode or cathode, thereby the supply of variable pressure and product gas can be flushed out of the respective electrode cells.

The valves 30 are shown in the figure before the inlet into the electrolytic cell, but can also be, for example, after the outlet of the electrolytic cell and / or at other locations of the anolyte 10 or catholyte circulation 20 be provided. Also, for example, a valve 30 lie in the anolyte before the inlet into the electrolytic cell, while the valve in the catholyte circuit 20 behind the electrolysis cell, or vice versa.

Another, in 7 illustrated exemplary electrolysis device for CO ₂ corresponds to the electrolysis device in 6 , in which case the cathode K is formed as a gas diffusion electrode through which flows. This electrolysis device is analogous to CO applicable.

By electrolysis or electrolysis, a gas mixture can be obtained, which is suitable as a starting gas for the production of propanol, propionaldehyde and / or propionic acid or their esters.

Since carbon dioxide electrolysis in the present case is a gas-to-gas electrolysis, the product gases usually also contain CO ₂ , which can easily be removed by gas scrubbing (pressurized water washing, absorption scrubbing). Thus, according to certain embodiments, the product gas from the electrolysis, particularly the CO ₂ electrolysis, is purified by gas scrubbing prior to being fed to the reaction for propanol, propionaldehyde and / or propionic acid, which is not particularly limited. The devices according to the invention thus comprise, according to certain embodiments, one or more gas scrubbers which are provided between the electrolysis devices, in particular the first and possibly second (CO ₂ ) electrolysis devices, and the first reactor for the reaction.

In the process of the invention, the reaction of CO and C ₂ H ₄ with H ₂ to propanol, propionaldehyde and / or the reaction of CO and C ₂ H ₄ with H ₂ O to propionic acid is not particularly limited and can be carried out according to known methods. According to certain embodiments, the respective reactions take place in water, which can already be used as solvent during the electrolysis, so that no separation of CO, C ₂ H ₄ and / or H ₂ from the water must take place before the reaction. Like the particular reaction, the first reactor used therefor, in particular in the devices according to the invention, is not particularly limited.

According to certain embodiments, the reaction of CO and C ₂ H ₄ with H _{2 takes place} by a hydroformylation reaction. According to certain embodiments, the reaction of CO and C ₂ H ₄ with corresponding equivalents of H ₂ to propanol, for example with [HCo (phosphine) (CO) ₃ ] as a catalyst. According to certain embodiments, the reaction of CO and C ₂ H ₄ with H ₂ O takes place by a hydrocarboxylation reaction, for example using nickel carbonyl as catalyst.

The hydroformylation is an ideal application for an ethene electrolyzer with the experimentally achieved product gas composition, since the "by-products" are needed. Since ethene, CO and H _{2 are} required equimolar, according to certain embodiments, for example, they are supplemented in addition to the product gas stream of the ethene electrolyzer. For this example, a CO ₂ - and / or CO and possibly a water electrolyzer can be used. Depending on the design and catalyst selectivity, the starting gas mixture for the hydroformylation can come from one or the combination of two or even three electrolyzers.

By combining an ethene, CO and water electrolyzer gas mixtures can be generated, which are basically suitable as feed for the hydroformylation, as well as for the production of propanol. The coupling of electrolysis and hydroformylation to produce propionaldehyde and also the coupling of electrolysis and propanol production are also economically particularly interesting because the individual gases do not need to be further worked up.

In principle, the coupling with all variants of the hydroformylation or propanol production is possible.

According to certain embodiments, the hydroformylation is carried out with, for example, biphasic, rhodium-catalyzed hydroformylation. It is preferably carried out in aqueous solution, wherein no drying of the product gas stream is required. According to certain embodiments, the gas is saturated with water, so aqueous electrolytes are used in the respective electrolysis. In the biphasic process, the Rh complex acting as a catalyst is dissolved in an aqueous phase. Since the produced aldehydes do not completely mix with water, the product separates at least partially as a second phase. In addition, the starting materials are gaseous. Therefore, this process can be operated continuously. This makes it particularly suitable for coupling with electrolysis systems, since electrolysers usually operate continuously. Accordingly, no complicated intermediate storage of the educt gases is necessary in the proposed coupling.

The reaction temperature of the hydroformylation to propionaldehyde is usually in the range of 60-80 ° C. Thus, this reaction can for example be operated at least partially or completely with the waste heat of the electrolyzers. This temperature profile, even according to certain embodiments, allows the distillation of the propionaldehyde (boiling point 49 ° C). The waste heat of the electrolyzer is therefore sufficient, if necessary, to operate the hydroformylation reactor and separate the propionaldehyde by distillation. Analogous considerations can be made in the production of propanol, which accordingly requires at least two equivalents of H ₂ .

The situation is similar in the case of a hydrocarboxylation of ethene, in which case, for example, water from an electrolyzer in which ethene and / or CO are dissolved can be used directly, in particular with nickel carbonyl. Again, a coupling with continuously operating electrolysis facilities is possible. This reaction can also be operated, for example, at least partially or completely with the waste heat of the electrolyzers.

Thus, according to certain embodiments, waste heat from the electrolysis of CO _{2 is used} in the hydroformylation reaction, the production of propanol, and / or the hydrocarboxylation reaction. A waste heat from the electrolyzer or the electrolyzers can be used for the mentioned methods for conversion to propanol, propionaldehyde and / or propionic acid, for example at slightly elevated temperatures below 100 ° C., preferably below 90 ° C., more preferably below 80 ° C.

It is also to be mentioned here that instead of reacting with water to give propionic acid, it is also possible to react with alcohol R-OH to give propynoic acid esters, where R is a substituted or unsubstituted, e.g. unsubstituted, organic radical of 1 to 20, e.g. 1 to 6, 1 to 4 or 1 to 2 C atoms, for example, a substituted or unsubstituted, e.g. unsubstituted, alkyl, aryl, alkylaryl or arylalkyl radical of 1 to 20, e.g. 1 to 6, 1 to 4 or 1 to 2 C atoms. The substituents are not limited insofar as they are not interfered with in the reaction, and may be, for example, halo, -OH, etc.

Thus, a process for the preparation of esters of propionic acid is also described, comprising:
Electrolysis of CO ₂ to CO and C ₂ H ₄ ; and
Reaction of CO and C ₂ H ₄ with ROH to give propionic acid esters, where ROH is as defined above. Again, the individual embodiments with respect to the electrolysis and implementation can be applied analogously, as well as with respect to a corresponding device.

Also described are an apparatus for producing propionic acid esters, comprising:
at least a first electrolysis device for the electrolysis of CO ₂ to CO and C ₂ H ₄ , which is adapted to produce CO and C ₂ H ₄ by electrolysis of CO ₂ ; and
at least one first reactor for reacting the CO and C ₂ H ₄ with ROH to propionic acid ester; and an apparatus for producing propionic acid esters, comprising:
at least one first electrolysis device for the electrolysis of CO ₂ and / or CO to C ₂ H ₄ , which is designed to produce C ₂ H ₄ by electrolysis of CO ₂ and / or CO;
at least one second electrolysis device for the electrolysis of CO ₂ to CO, which is designed to produce CO by electrolysis of CO ₂ ; and
at least one first reactor for reacting the CO and C ₂ H ₄ with ROH to propionic acid ester, wherein ROH is in turn as defined above.

In a second aspect, the present invention relates to an apparatus for producing propanol, propionaldehyde and / or propionic acid, comprising: at least one first electrolyzer for the electrolysis of CO ₂ to CO and C ₂ H ₄ , which is designed to CO and C ₂ To produce H ₄ by electrolysis of CO ₂ ; and at least a first reactor for reacting the CO and C ₂ H ₄ with H ₂ to propanol and / or propionaldehyde, and / or for the reaction of CO and C ₂ H ₄ with H ₂ O to propionic acid.

In such a structure, it is possible that, for example, an electrolytic cell is operated with alternating cathodes to produce various product gases, but this requires intermediate storage of product gases, or it is possible to operate an electrolysis device having a plurality of electrolytic cells which may, for example, operate in parallel For example, the number of different electrolytic cells may also be adjusted to obtain a near-ideal reactant gas mixture by mixing the products of the electrolysis cells, which may then be subjected to a hydroformylation reaction or a hydrocarboxylation reaction. Also, sequentially operating electrolysis cells for the production of ethene from CO ₂ via the intermediate CO are possible.

According to certain embodiments, the first electrolysis device comprises at least one electrolytic cell having a cathode comprising or consisting of copper and at least one electrolysis cell having a cathode comprising or consisting of a metal selected from the group consisting of Au, Ag and / or Zn, preferably Ag. As a result, eg, parallel, ethene and CO and possibly also H ₂ can be produced efficiently.

In a further aspect, the present invention relates to a device for producing propanol, propionaldehyde and / or propionic acid, comprising:
at least one first electrolysis device for the electrolysis of CO ₂ to C ₂ H ₄ , which is adapted to produce C ₂ H ₄ by electrolysis of CO ₂ ;
at least one second electrolysis device for the electrolysis of CO ₂ to CO, which is designed to produce CO by electrolysis of CO ₂ ; and
at least one first reactor for the reaction of CO and C ₂ H ₄ with H ₂ to propanol and / or propionaldehyde, and / or for the reaction of CO and C ₂ H ₄ with H ₂ O to propionic acid.

Optionally, subsequent oxidation of the propanol and / or propionaldehyde with anodically produced oxygen to propionic acid in a suitable reactor can take place in the devices according to the invention.

In this case, CO and ethylene-ethylene, for example, also from CO-can be prepared in parallel in various electrolysis devices, whereby the efficiency of the method according to the invention can be increased when carried out in such a device.

According to certain embodiments, the first electrolysis device comprises a cathode comprising or consisting of copper, and the second electrolysis device has a cathode comprising or consisting of a metal selected from the group consisting of Au, Ag and / or Zn, preferably Ag. As a result, in turn, for example, in parallel, ethene and CO and optionally also H ₂ can be produced efficiently. As a substrate for ethylene and hydrogen production is suitable CO ₂ , but also CO.

According to certain embodiments, the devices according to the invention further comprise at least one third electrolysis device, which is designed to provide H ₂ by an electrolysis of CO ₂ and / or CO and / or an electrolysis of H ₂ O. With a combination of two or in particular three electrolysis devices, a suitable mixture for the hydroformylation and / or propanol production can be produced with high efficiency.

In the first reactor, a hydroformylation reaction, a reaction for producing propanol, or a hydrocarboxylation reaction may be carried out in the apparatus of the present invention, and the first reactor is not particularly limited here.

Furthermore, the devices according to the invention can comprise at least one heat conduction which is designed to supply waste heat from the electrolysis of CO _{2 to} the first reactor. A corresponding heat conduction can also provide waste heat from other electrolysis devices, eg CO and / or H ₂ O electrolysis. Such a heat conduction can also be provided for supplying waste heat to a second reactor for the conversion of propanol and / or propionaldehyde to propionic acid. The heat pipes are not particularly limited. Instead of heat pipes, a direct contact between a respective (first, second and / or third) electrolysis device and a respective (first and / or second) reactor may be provided.

According to certain embodiments, the devices of the invention comprise a second reactor for reacting propanol and / or propionaldehyde to propionic acid formed therefor is to convert propanol and / or propionaldehyde to propionic acid. Also, this reactor is not particularly limited insofar as it permits the corresponding reaction, for example, oxidation.

With the devices according to the invention, the inventive method can be carried out. In this respect, the respective electrolysis devices and reactors correspond, for example, to those mentioned in connection with the process according to the invention.

In addition, the device according to the invention may comprise further components which are present in an electrolysis plant or electrolysis device, that is to say different cooling in addition to the current source for the electrolysis. and / or heating devices, etc., as well as components of a reactor such as cooling and / or heating devices, as well as connections between the electrolysis devices and reactors, for example in the form of pipes, etc. These other components of the device, such as an electrolysis system, are not further limited and may be provided appropriately.

The above embodiments, refinements and developments can, if appropriate, be combined with one another as desired. Further possible refinements, developments and implementations of the invention also include combinations of features of the invention which have not been explicitly mentioned above or described below with regard to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

The invention will be illustrated below with reference to some exemplary embodiments which, however, do not limit the same.

Examples

The entire method according to the invention is shown schematically by way of example in FIG 8th shown for a hydroformylation.

In this case, energy E, for example from renewable energy sources and / or excess current, in the respective electrolysis for Cu-catalyzed production of C ₂ H ₄ , optionally with CO and H ₂ as by-products, from CO ₂ , for Ag-catalyzed production of CO , optionally with H ₂ as by-product, from CO ₂ , and used for PEM electrolysis of water to H ₂ . These starting materials are then mixed and subjected to hydroformylation 1 converted to propionaldehyde.

The present invention provides a highly integrated, energetically tuned process for producing propionaldehyde and propionic acid without fossil resources and high temperature processes.

Since all required components can be generated electrochemically from CO ₂ , the process is independent of fossil carbon sources. The energy input is also mainly concentrated in the electrochemical steps, which significantly increases the energy efficiency. Last but not least, a versatile C3 module is obtained from the energy and worthless C1 component CO ₂ . An ethylene / CO / H ₂ mixture would not be salable without costly separation, while the C3 derivatives from the combined process would be a directly salable product.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102015203245 [0019]
• DE 102016200858 [0040]
• DE 102015212504 [0049]

Cited non-patent literature

• C. Vayenas, et al. (Eds.), Modern Aspects of Electrochemistry, Springer, New York, 2008, pp. 89-189 [0018]

Claims (15)

Process for the preparation of propanol, propionaldehyde and / or propionic acid, comprising: electrolysis of CO ₂ to CO and C ₂ H ₄ ; and reacting the CO and C ₂ H ₄ with H ₂ to give propanol and / or propionaldehyde, and / or reacting the CO and C ₂ H ₄ with H ₂ O to give propionic acid. The method of claim 1, wherein H _{2 is provided} by the electrolysis of CO ₂ and / or CO and / or an electrolysis of H ₂ O. The method of claim 1 or 2, wherein in the electrolysis of CO ₂ also anodic an oxygen species is generated, and the oxygen species is reacted with propanol or propionaldehyde to propionic acid. The method of claim 3, wherein the oxygen species is oxygen and / or a peroxide. Method according to one of the preceding claims, wherein the production of C ₂ H ₄ from CO ₂ and / or CO by electrolysis takes place on a copper-containing cathode. A process according to any one of the preceding claims wherein the production of CO from CO _{2 is} by electrolysis at a cathode comprising a metal selected from the group consisting of Au, Ag and / or Zn. Method according to one of the preceding claims, wherein the reaction of CO and C ₂ H ₄ with H _{2 takes place} by a hydroformylation reaction and / or a reaction for propane production, and / or wherein the reaction of CO and C ₂ H ₄ with H ₂ O by a hydrocarboxylation reaction takes place. A process according to claim 7, wherein waste heat from the electrolysis of CO _{2 is used} in the hydroformylation reaction and / or propane production and / or hydrocarboxylation reaction. An apparatus for producing propanol, propionaldehyde and / or propionic acid, comprising: at least a first electrolyzer for the electrolysis of CO ₂ to CO and C ₂ H ₄ , which is designed to produce CO and C ₂ H ₄ by electrolysis of CO ₂ ; and at least a first reactor for reacting the CO and C ₂ H ₄ with H ₂ to propanol and / or propionaldehyde, and / or for the reaction of CO and C ₂ H ₄ with H ₂ O to propionic acid. The device of claim 9, wherein the first electrolyzer comprises at least one electrolytic cell having a cathode comprising copper and at least one electrolytic cell having a cathode comprising a metal selected from the group consisting of Au, Ag and / or Zn. Apparatus for the production of propanol, propionaldehyde and / or propionic acid, comprising: at least one first electrolyzer for the electrolysis of CO ₂ and / or CO to C ₂ H ₄ , which is designed to produce C ₂ H ₄ by electrolysis of CO ₂ and / or to produce CO; at least one second electrolysis device for the electrolysis of CO ₂ to CO, which is designed to produce CO by electrolysis of CO ₂ ; and at least one first reactor for reacting the CO and C ₂ H ₄ with H ₂ to propionaldehyde and / or propanol, and / or for the reaction of CO and C ₂ H ₄ with H ₂ O to propionic acid. The apparatus of claim 11, wherein the first electrolyzer comprises a cathode comprising copper, and the second electrolyzer comprises a cathode comprising a metal selected from the group consisting of Au, Ag, and / or Zn. Device according to one of claims 9 to 12, further comprising at least one third electrolysis device which is adapted to provide H ₂ by an electrolysis of CO ₂ and / or CO and / or an electrolysis of H ₂ O. Apparatus according to any one of claims 9 to 13, further comprising a heat pipe adapted to supply waste heat from the electrolysis of CO _{2 to} the first reactor. Apparatus according to any one of claims 9 to 14, further comprising a second reactor for reacting propanol and / or propionaldehyde to propionic acid, which is designed to react propanol and / or propionaldehyde to propionic acid.

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